What are the categories of prescribed prayer times?
Chapter on Prayer Times
Al-Mughni
Book of Prayer
Primary text
The prescribed prayer times are divided into three categories: the time of virtue (Fadhila), the time of permissibility (Jawaz), and the time of necessity (Darura). The times of permissibility and necessity have been previously mentioned. The time of virtue is that which Al-Kharqi mentioned, where Ahmad stated that the beginning of the time is more beloved, except for two prayers: the Isha prayer and the Dhuhr prayer, which should be delayed during intense heat. The Prophet, peace be upon him, customarily prayed Dhuhr when the sun passed its zenith (Hajir/Al-Ula), and delayed Isha. He performed Fajr prayer while it was still dark (Ghalas), reading between sixty and one hundred verses.
Supporting text
Jabir reported that the Prophet, peace be upon him, prayed Dhuhr early (Hajira), Asr while the sun was bright and clear, Maghrib immediately when due, and Isha sometimes early and sometimes late depending on whether people had gathered. Regarding the morning prayer, the Prophet prayed it while it was still early dawn.